This grant is submitted in response to the request for research grants on human infertility published in NIH Guide for Grants and Contracts, Volume 5, No. 19, November 15, 1976. The objective of this proposal is to develop and evaluate new diagnostic tests which will more accurately predict the fertility of human semen. The primary assay will examine the ability of the human spermatozoa to penetrate mouse ova denuded of the zona pellucida. This indirectly evaluates the ability of the spermatozoa to undergo capacitation and the acrosome reaction. Thus the assay may also provide insight into the nature of the defect(s) in the spermatozoa of infertile men. In addition, the motility of sperm used for the ova penetration assays will be determined by an objective, time lapse photographic method. The semen of fertile men will be evaluated initially. Then the spermatozoa of male partners of carefully evaluated infertile couples will be assayed and the results correlated with clinical examinations, routine semen analysis, and future fertility.